This invention relates generally to doorbell systems and particularly to an automatic doorbell driver that utilizes the power, wiring, and primary load of a conventional doorbell system.
Conventional doorbell systems in buildings, typically residences, throughout the United States and elsewhere are hardwired and comprise a transformer, a primary load, and a pushbutton. The transformer lowers standard household AC voltage to a level required to operate the primary load. The primary load is an electromagnetic or electronic sound device that operates on low voltage and is typically a bell, buzzer, or chime. The pushbutton is a typically a normally open switch. System activation requires physical contact with the pushbutton. Manual depression of the pushbutton closes an electrical circuit causing the primary load to energize. Often there is no feedback provided to inform the activator that the primary load has been energized.
Considerations of convenience, sanitation, security, and/or simply surprise and delight have led to the development of automatic doorbell systems. That is, doorbell systems that can automatically detect a person's presence outside a doorway and alert a person inside when such a detection occurs. Both U.S. Pat. No. 4,236,147 to Calvin (1980) and U.S. Pat. No. 5,428,388 to von Bauer et al. (1995) disclose such a system.
Unfortunately, all of the systems devised thus far, including Calvin's and von Bauer's, have a significant disadvantage that has prevented their widespread application. That is, they are either independent or predominately independent systems that do not, or do not sufficiently, interface with or complement a conventional doorbell system. As a result, they are complex, difficult to install, expensive, redundant, and/or require periodic maintenance (e.g., battery replacement).